Apex domains cannot have CNAME records.
Question and response
Question
dig gaztelecom.ru. NS
Answer
gaztelecom.ru. 5 NS ns2.gaztelecom.ru.
gaztelecom.ru. 5 NS ns.gaztelecom.ru.
Authority
The response has no authority records.
Additional
ns.gaztelecom.ru. 5 A 87.237.137.2
ns2.gaztelecom.ru. 5 A 87.237.139.42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0